Ion injection device for thermonuclear plasma apparatus



June 11, 1963 F. PREvoT 3,093,765

ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS Filed March 22, 1960 6 Sheets-Sheet 1 FIG. I

June 11, 1963 F. PREVOT 3,093,765

ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS Filed March 22, 1960 G Sheets-Sheet 2 June 11, 1963 FfPREvoT ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS 6 Sheets-Sheet 3 Filed March 22, 1960 FIG.3

F. PREVOT June 11, I963 ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS 6 Sheets-Sheet 4 Filad larch 22, 1960 FIG.6

June 11, 1963 F. PREVOT 3,

ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS Filed March 22, 1960 6 Sheets-Sheet 5 F IG.9

June 11, 1963 F. PREVOT 3,

ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS Filed March 22, 1960 6 Sheets-Sheet 6 FIG. 70

United States Patent ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS FrancoisPrvot, Antony, France, assignor to Commissariat a lEnergie Atomique, Paris, France Filed Mar. 22, 1960, Ser. No. 16,830

Claims priority, application France Apr. 20, 1959 12 Claims. (Cl. 313-63) 7 The present invention relates to apparatus used for forming a plasma, i.e an ionized medium, wherein thermonuclear fusion reactions take place. It pertains more particularly to devices for the injection of fast ions in such apparatus for the formation of a high temperature and high density plasma, confined in a magnetic field.

In a certain known apparatus (such as apparatus DC-X at Oak Ridge, Tennessee, USA.) the ionized particles, accelerated by appropriate means, are injected in the plasma formation zone shaped as a linear beam of molecular ions, the molecular ions being dissociated into atomic ions by an electric arc and then captured in the magnetic field of confinement crossed by the arc. Such an apparatus has shortcomings which are essentially due to the method of injecting the ions.

The particles being injected in the form of a linear beam, the intensity of that beam is limited by the ion source, the flow and efiiciency in molecular ions of the source being limited. The intensity is also limited by the spacial charging which has a tendency to expand the beam, and by the requirement that the path be well defined. It follows from this limitation in intensity that the plasma thus obtained is of low density. On the other hand, the presence of a critical intensity in the injected ion current, which intensityis a function of the energy of these ions and below which the apparatus will not operate requires the use of a high energy value thus involving technological difficulties of construction which do not improve the formation of the plasma.

It is also necessary in an apparatus of this type, to have a well defined accelerating tension of the ions, necessitating an expensive control system. Finally, etficiency remains low due to the fact that the ions which were not captured in the plasma formation zone are lost after onlyone passage through said zone and, furthermore, the thermalization, i.e., the creation of a plasma by dissociation and capture of ionized particles, is rendered more difficult by the high energy combined with the low intensity of the beam and its unidirectional characteristic. It is well to note also the possibility of instability due to the anisotropy of the ion velocities.

The instant invention therefore proposes a device for injecting and capturing ionized particles within a magnetic field, to obtain a high temperature plasma which obviates these various inconveniences while being simple inmanufacture and safe in operation- Tln's device for injecting and capturing ionized particles is essentially characterized in that it comprises an annular ion source combined with an annular acceleration electrode coaxial to said source and creating a sheetlike ion beam; the confinement magnetic field of axial symmetry being coaxial with the ion source and the electrode.

In one embodiment of the invention, the acceleration electrode is simple, roughly having the form of a split ring and being supported at the interior of the casing of the apparatus by high tension insulators distributed along a circumference and alternating with insulators supporting the ion source.

A second embodiment of the simple acceleration electrode type, by the use of appropriate position-regulating means for the high tension insulators or their internal elements, changes the form of the injected ion sheet, which can either be located in a plane normal to the axis of symmetry of the apparatus or in a cone of revolution having an axis coinciding with the said axis of symmetry and having an adjustable apex angle. This arrangement multiplies the passages of a given particle along the axis.

A third embodiment is characterized in that the acceleration electrode, housed within a circular insulator containing the ion source, is of the gradient type, which permits the use of injection tensions and acceleration fields greater than in the first embodiments.

Whichever embodiment is being considered, the device of the invention is characterized in that the beam of injected ions has a form of a Sheet, plane or conical. This beam therefore has a high intensity which leads to the formation of high density plasma. The intrinsic very high intensity of the beam ensures on the other hand that the operating condition of the apparatus mentioned above, namely the necessity that the injection intensity be higher than a critical intensity, is satisfactory. This enlarges considerably the choice of the energy of the ion and permits in particular, to use the most favourable value for the desired temperature.

The device of the invention offers other advantages.

It does away for instance, with the necessity of stabilizing the acceleration tension and the magnetic field due to the fact that, by virtue of its symmetry, it has a focusing property independent of the energy of the ions, starting with a certain value. It leads to a high energy efficiency resulting, on the one hand, from the ions having several passages in the magnetic field and, on the other hand, from the increase in dissociation efficiency in a single passage; the particles being capable of dissociation among.

themselves on account of their higher density and the isotropy of the velocities. Finally, the possible weakening of the injection energy and the symmetry of the device, in consequence of which the paths of the particles all have one common point at the center, render the heating of the beam more rapid and eflicient and can remove the instability mentioned above.

Other characteristics and advantages of the invention will appear in the following description having reference to the attached drawings wherein:

FIG. 1 shows schematically, in axial vertical section, an apparatus provided with an injection device of the invention;

FIG. 2 is a out along line A-A of FIG. 1;

FIG. 3 schematically shows a path of a particle projected against the plane containing the axis of revolution XX of the apparatus;

FIG. 4 shows a projection of the path of FIG. 3 on a plane normal to axis XX;

FIG. 5 schematically shows the successive paths of one particle making several passages on the axis;

FIG. 6 shows one type of variable tension applied to the ion source capable of defining the movement shown on FIG. 5;

FIG. 7 shows a method of attachment of the insulator supports;

FIG. 8 shows an arrangement of the coils creating the confinement magnetic field in the case of a conical ion beam;

FIG. 9 shows another possible arrangement of the confinement coils;

FIG. 10 shows, in axial vertical section, an apparatus provided with another embodiment of the device of the invention.

It can be seen, on FIG. 1, shown schematically in axial vertical section, an apparatus used for the creation of a plasma, provided with the injection device which is the object of the present invention.

This apparatus comprises, in known fashion, a cylindrical fluid proof casing 1 of axis XX, containing a chamber 2 defined by a housing 3 of heat resistant stainless steel. The enlarged central section 4 of chamber 2 constitutes the plasma formation zone. The confinement magnetic field is created by two magnetic coils 5 and 6, respectively located on either side of enlarged part 4, coaxially of chamber 2. The coils are cooled by fluid flowing in tubes 7, 8, 9 and 10'. Two electrodes 11 and 12 are used to create a dissociation arc in the plasma formation zone.

Housing 3 is surrounded by a cooling coil (normal operation) or a heating coil 13 (during gas removal). Vacuum is produced in the casing 1 by means of two identical groups each comprising a mechanical pump :14 and a diffusion pump 15 associated with a liquid nitrogen trap, having a condensation screen and a valve. The primary vacuum thus produced in the casing 1 is in the order of 10* mm. of Hg. Similarly, chamber 2 is placed under vacuum by means of two identical groups, each having a mechanical pump 16 and a diffusion pump 17 associated with a liquid nitrogen trap, having a condensing screen and a valve. It is thus possible to produce in chamber 2, a secondary vacuum in the order of 10- mm. of Hg.

In accordance with the invention, the ion injection device used in the apparatus has an annular shape. It is essentially composed of a circular source of ions 18 and a middle electrode 19, also circular, both of which are centered on axis XX of the apparatus. The relative arrangement of these components is best seen on FIG. 2, which is a sectional view along line A-A of FIG. 1. The ion source 18 is of any adequate type giving ions which may be molecular. It has the approximate shape of an annular channel, the opening of which, formed as a circular slit, is turned toward the axis of the apparatus.

High tension insulators are evenly distributed around the cylindrical wall of easing 1 with their axis located in,

the plane of symmetry of the apparatus normal tothe axis XX. Half the insulators, identified at 20 on FIG.;

This'method of attachment and feeding of the ion source and of the middle electrode is not restrictive and it is possible, within the spirit of the invention, to consider other appropriate alternatives, as, for example, using a different number and type of insulators.

The confinement coils 5 and 6 (FIG. 1) are partially surrounded by a ferromagnetic frame 26, cut off in the plane of symmetry of the apparatus to form a clearance '27 between the polar extensions 28 and This frame 26 is intended to concentrate the lines of magnetic force in the vicinity of coils 5 and 6 in a pattern similar to that shown by the two lines of force 30 and 31. The ferromagnetic frame 26 prevents scattering of the lines of force, all of which must close within the ion source, it being necessary that the total magnetic flux embraced by the annular ion source be zero.

A circular slit 32 (FIG. 1) in the plane of symmetry of the apparatus allows entry of the ion beam into the enlarged portion 4 of chamber 2. An acceleration electrode 33 is supported by the ferromagnetic frame 26 and at the same potential thereof, that is, the potential of the mass.

Vacuum providing components 14, 15, 16 and 17 permit the maintenance of a vacuum in the order of 10* mm. of mercury at the interior of the casing 1 and in the order of 10- mm. in the chamber 2.

The arrangement of the confinement coils gives to the magnetic field in the area of injection, an axial symmetry; an essential characteristic of the device of the invention. Outside the injection area, the magnetic field may have any shape, provided that this does not modify the conditions indicated above with regard to the injection Zone.

The annular source 18 ejects molecular ions, which are accelerated by the electric field maintained between the source and the injection Zone by the circular electrodes, such as 19 and 33. Any charged particle, the path of which, outside the magnetic field, is contained in a meridian plane containing the axis of symmetry XX, passes by this axis if it achieves a minimum energy con dition. FIGURE 3 schematically shows the pattern of the confinement magnetic field outlined by the lines of force 34, 35, 36 and 37, in a plane containing the axis of revolution XX, and a path of particle 38 entering the field in a certain meridian plane and moving out of the field in a different meridian plane. FIG. 4 shows this trajectory projected on a plane normal to axis XX. The circumferences shown in dashed line define the magnetic field Zones in one direction and in the other, the circumference shown in dotted line represents the trajectory of the captured particle if it is dissociated on the axis.

' All the particles, the trajectories of which lie outside the magnetic field ofmconfinement and generate a cone coaxial to magnetic field, will effectively pass by the axis. The trajectories may, particularly, be perpendicular to the axis and consequently contained in a plane perpendicular to the axis. This is accomplished by the device of FIGS. 1 and 2, where the particles emitted by source 18 have trajectories contained in a plane perpendicular to the axis X-X, the ion beam having the form of a plane sheet. The molecular ions emitted by source .18 are dissociated on the axis, for example, by means of a carbon arc, a hydrogen arc, etc. The atomic ions thus formed have a mass twice as small and consequently a radius of gyration twice as small in-the field of confinement where they are confined if the initial energy of the dissociated ions coincide with a condition of maximum value. (Maximum energy=four times minimum energy).

Apart from its circular shape, the ion source may be of any appropriate type whatever, high frequency source, arc

source, etc. The embodiment shown in FIGS. 1 and 2 is suitable because of the arrangement of the high tension insulation for relatively moderate tensions, for example, up to 200 kv. It is not necessary that the acceleration tensions be subjected to regulation since all the trajectories pass by the axis of symmetry, independently of the energy of the particles.

If an ion is not dissociated, it moves out of the magnetic field and returns to the source, where it may leave again, following a second trajectory similar to the first one and consequently, pass again on the axis where it is' afforded another chance to dissociate. It may also be lost in the source. In order to avoid this second possibility and obtain several passages on the axis, several. various arrangements may be considered.

. the insulator.

It is possible, for instance, by holding an ion beam in the form of a plane sheet normal to the axis of symmetry, to produce a rapid increase of the tension at the source. This way the non-dissociated particle turns back before reaching and hitting the source. The successive trajectories obtained thereafter have the form shown on FIG- URE 5 where 18 is theinterior limit of the source. A simple method to achieve this result, without excessively complicating the installation while varying the tension at thesouroe, consistsin. giving to this tension a saw tooth shape, as is represented on FIGURE 6, where tension thiscomponent, enter a zone of stronger flux where they remain for a certain time. The zones of weak magnetic flux are created by modifying the layout, the number or the supply to the confinement coils.

It is possible to obtain an ion beam of conical shape by using an embodiment of j the invention wherein the insulators 20 and 23, or only their internal elements respectively support the ion source and the middle electrode, may be displaced parallel to the axis XX to occupy positions ofi-set in relation to the plane of symmetry normal to the axis. In this embodiment of the invention, the setting of the insulators may be made as indicated in FIG. 7. Opening 39 of easing 1, which, for example,

receives an insulator 20, is provided with a flange 40 apertured with elongated anchorage holes 41. The body of the insulator, the base of which is schematically shown, also has .a flange 42, ,apertured with holes 43. Bolts 44 hold the two flanges in fixed relation to one another and compress a sealing ring 45 therebetween. The elongated holes .41 allow for a relative displacement of the flanges 40 and 42 and consequently allow change of the position of the insulators such as 20 and 23. For greater accuracy,

, for instance, for the source and the middle electrode fastened on the casing in .a position corresponding to the formation of a beam in the form a conical sheet.

In a case where the ion beam has a conical shape, the

, zones of strong and weak magnetic flux may be obtained in two different ways. It ispossible to obtain a deviation of the magnetic lines of torce by means of magnetic shunts whereby par-t of the lines of force close in around the coils 5 and 6 without going from one to the other, as

shown on FIG. 8. Themagnetic flux is then more intense in zoneA than in zone B. On the other hand, it is possible to increase the number ofcoils as. shown in FIG.

.9, and reversethe flow of current, for example, in coils 46fand 47. The lines of force distribute themselves then as indicated, which will again give a weaker flux in in- )ternal zone B than in internal zone A'.

In a third embodiment of the invention, as shown in FIG. 10, the device differs from that shown in FIG. 1 mainly in the arrangement of the ion source and the acceleration electrode. These are enclosed within a single circular insulator 48, which fcanbe made up of several elements. The ion source49 is located at the bottom of It has an annular form and emits an ion beam in a plane sheet normal to axis XX. The accelerlation electrode comprises several levels, such as 50, distributed between the ion source and the casing 1 of the apparatus. This arrangement permits the use of higher tension than in the first embodiment greater than 200 kv. The apparatus has the same elements as in the embodiment of FIG. 1 and the elements have been identified by the same reference numeral.

In certain embodiments of the invention, the dissociation arc can be removed, due to the fact that the plasma which is obtained and which is of high density, will itself cause dissociation of the particles reaching its sphere of action.

Finally, the invention overcomes the inconvenience of lost particles by exchange of load lead-ing to a neutralization of ions, which causes heating and superficial evaporization of the enclosing walls with generation of gas and various impurities. In the embodiment of the in vention, the neutralized particles are in a greater part in the injection plane, in the case of the injection in plane sheet, and because of this move out of zone 4, or plasma formation zone. On the other hand, the electric field due to the spacial loading of the injected beam modifies the movement in prior known devices, whereas, axial tocal-ization is not changed in the case of the present invention.

It will be understood that the invention is not limited to the embodiments described and shown which were given only as examples and to which numerous changes may be made without departing from the spirit of the invention.

The embodiments of the invent-ion in which an exclusive property or privilege is claimed are defined as follows:

1. Ion injection device for thermonuclear plasma apparatus including an enclosure under vacuum, an annular source of ions, an annular accelerating elect-rode for said ions, production and confinement means for the plasma, means for dissociation of molecular ions centered on the axis of said source, said electrode being coaxial with said source and creating with said source anion beam in sheet form, said means including annular electric coils creating a confinement magnetic field of axial symmetrical and coaxial with said ion source and said acceleration electrode, a ferromagnetic frame surrounding said confinement coils and an annular air gap in said frame for the passage of the ion beam.

2. A device as described in claim 1 including high tension insulators spaced on the periphery of said enclosure supporting said acceleration electrode within said enclosure andinsulators supporting said ion source alternating with said first insulators.

3. A device as described in claim 1 including an annular insulator fixed to the periphery of said enclosure and means for mounting said acceleration electrode in said insulator, said annular ion source being mounted in said insulator away from said enclosure.

4. A device as described in claim 2 wherein said insulators being displaceable parallel to the axis of symmetry of said ion source whereby said ion source can create selectively a beam in a plane normal to the axis and a beam in form of a conical sheet.

5. A device as described in claim 4 wherein said insulators are located in an ionic plane sheet.

6. A device as described in claim 4 wherein said insulators are located in a conical sheet.

7. A device as described in claim 1 including at least least two of said electric coils creating the confinement magnetic field, said coils being fed in reverse directions to divert lines of the magnetic field.

8. A device as described in claim 1 including magnetic shunts for said electric coils to divert lines of the magnetic field.

9. A device as described in claim 1 wherein the tension of said ion source is varied in a sawtoothed voltage wave.

10. A device as described in claim 1, said course of 7 ions emitting from an internal surface, said means for axis successively traverse two regions where the magnetic 12. A device as described in claim 10, the tension of field is directed parallel to the axis of said source in one i i source g a saw-toothed voltage wave- .direction in one region and in the opposite direction to a the other region, the total flux on a surface'bearing on References Clted the file of vthls patent said source *being approximately zero. a 5 UNITED STATES PATENTS ,11. A device as described in claim 10, said acceleration 29202 5 B611 1 Jam 5 1960 electrode and said source of ions being so disposed vthat 2,920,236 Chambers et a1. Jan. 5, 1960 the sheet of ions is conical. 2;927,23 2 'Luce Mar. 1, 1960 

1. ION INJECTION DEVICE FOR THERMONUCLEAR PLASMA APPARATUS INCLUDING AN ENCLOSURE UNDER VACUUM, AN ANNULAR SOURCE OF IONS, AN ANNULAR ACCELERATING ELECTRODE FOR SAID IONS, PRODUCTION AND CONFINEMENT MEANS FOR THE PLASMA, MEANS FOR DISSOCIATION OF MOLECULAR IONS CENTERED ON THE AXIS OF SAID SOURCE, SAID ELECTRODE BEING COAXIAL WITH SAID SOURCE AND CREATING WITH SAID SOURCE AN ION BEAM IN SHEET FORM, SAID MEANS INCLUDING ANNULAR ELECTRIC COILS CREATING A CONFINEMENT MAGNETIC FIELD OF AXIAL SYMMETRICAL AND COAXIAL WITH SAID ION SOURCE AND SAID ACCELERATION ELECTRODE, A FERROMAGNETIC FRAME SURROUNDING SAID CONFINEMENT COILS AND AN ANNULAR AIR GAP IN SAID FRAME FOR THE PASSAGE OF THE ION BEAM. 